1. Field of the Invention
The present invention relates to a multilayer feedthrough capacitor used in a noise filter etc. designed not only to deal with noise of the common mode and noise of the differential mode, but also to reduce the equivalent serial inductance (ESL) more and thereby effectively eliminate noise in the high frequency band, more particularly one suitable for an information processing device or communications device.
2. Description of the Related Art
In recent years, the majority of information processing devices and communications devices have become digitalized. Further, along with the higher speeds of processing accompanying the improvements in information processing capabilities, there has been remarkable progress in raising the frequencies of the digital signals handled by these devices. Therefore, the noise produced from these devices also tends to increase more in the high frequency band. On the other hand, efforts are being made to make these devices more portable. Along with this, further reduction in the size and weight of these devices has become desired.
To deal with the noise, most electronic equipment use electronic devices able to prevent electromagnetic wave interference or suppress unnecessary voltage fluctuations. As these electronic devices, due to such a situation, electronic devices which are small in size, light in weight, and deal with noise in the high frequency band are being sought. As such electronic devices, in general, multilayer ceramic capacitors are currently being used.
In multilayer ceramic capacitors, however, the parasitic component, that is, the ESL, obstructs the noise eliminating effect in the high frequency band, so the effect has become insufficient along with the increasingly higher frequencies of the operating frequencies of electronic equipment. That is, capacitors having large ESLs such as the conventional multilayer ceramic capacitors are increasingly becoming unable to sufficiently handle the higher frequencies of recent years.
For example, as a conventional capacitor able to reduce the ESL, a multilayer type feedthrough capacitor (multilayer feedthrough capacitor) has been developized and is in general use. A multilayer feedthrough capacitor 110 according to the prior art will be described below based on FIG. 12 to FIG. 15.
The multilayer feedthrough capacitor 110, as shown in FIG. 13, has an internal conductor 112 having branch parts 112A and 112B led out toward two facing side surfaces. A dielectric sheet 124 formed on its surface with an internal conductor 114 led out to two side surfaces different from the two side surfaces where the branch parts 112A and 112B are led out has stacked with it a dielectric sheet 122 formed on its surface with the internal conductor 112. Dielectric sheets not formed with internal conductors are stacked above and below that stack in the stacking direction. This stack is then fired to form the stack 120 shown in FIG. 12.
As shown in FIG. 12, two facing side surfaces of the stack 120 are formed with terminal electrodes 131 and 132 which are connected to the branch parts 112A and 112B of the internal conductor 112. Further, the other two facing side surfaces of the stack 120 are formed with terminal electrodes 133 and 134 connected to the branch parts of the internal conductor 114. As shown in FIG. 14, the terminal electrodes 131 and 132 can be connected to for example the ground side, while the terminal electrodes 133 and 134 can be connected to the signal transmission paths.
A circuit diagram for dealing with noise in the common mode and differential mode using this conventional multilayer feedthrough capacitor 110 is shown in FIG. 15. As shown in FIG. 15, three multilayer feedthrough capacitors 110 are used to configure a circuit for reducing noise.
However, even in these multilayer feedthrough capacitors 110, currents flow in the directions shown by the arrows in FIG. 13, so there is an ESL of a certain magnitude. Therefore, such conventional multilayer feedthrough capacitors 110 are increasingly becoming unable to handle the higher frequencies of recent years and capacitors able to reduce the ESL further are becoming required.
Further, to deal with the higher density mounting accompanying the smaller sizes of electronic equipment, demand is rising for array type multilayer capacitors combining a plurality of capacitors.
Note that in multilayer capacitors, it is known to make the shape of the pattern of the internal conductor a substantially T-shape as shown in Japanese Unexamined Patent Publication (Kokai) No, 59-29413 and Japanese Unexamined Patent Publication (Kokai) No. 3-37850. These publications, however, do not disclose the idea of passing currents in opposite directions in internal conductors adjacent in the stacking direction so as to reduce the ESL.
Further, as shown in Japanese Unexamined Patent Publication (Kokai) No. 2000-58376, the idea has been proposed of reducing the ESL by optimizing the ratio of dimensions of the internal conductor in the capacitor. Further, as shown in Japanese Examined Patent Publication (Kokoku) No. 6-58861, Japanese Unexamined Patent Publication (Kokai) No. 8-55758, and Japanese Unexamined Patent Publication (Kokai) No. 2001-189234, the idea is known of passing currents in the opposite directions in an internal conductor of a capacitor.
However, these publications do not disclose that it is possible to reduce the noise of both the common mode and the differential mode in a multilayer feedthrough capacitor and to further reduce the ESL so as to improve the effect of elimination of high frequency noise.
An object of the present invention is to provide a multilayer feedthrough capacitor able to reduce both noise of the common mode and differential mode and able to further reduce the ESL so as to improve the effect of elimination of high frequency noise.
To achieve the above object, according to a first aspect of the present invention, there is provided a multilayer feedthrough capacitor comprising:
a first internal conductor arranged in a dielectric body,
an intermediate internal conductor arranged in the dielectric body and stacked with the first internal conductor via a ceramic layer,
a second internal conductor arranged in the dielectric body and stacked with the intermediate internal conductor via a ceramic layer,
a first terminal electrode formed at an outside surface of the dielectric body and connected to the first internal conductor,
a second terminal electrode formed at the outside surface of the dielectric body and connected to the second internal conductor, and
an intermediate terminal electrode formed at the outside surface of the dielectric body and connected to the intermediate internal conductor.
Preferably, the first internal conductor and the second internal conductor have currents passing through them in opposite directions.
Preferably, inside the dielectric body, the intermediate internal conductor is stacked between the first internal conductor and second internal conductor via the ceramic layers.
Preferably, the first internal conductor is formed with a pair of branch parts led out toward two opposite outside surfaces of the dielectric body, and each of the branch parts is connected to a pair of first terminal electrodes.
Preferably, the first internal conductor has a rectangular pattern slightly narrower than the ceramic layer forming the dielectric body, and
the pair of branch parts are formed at one end of the rectangular pattern in the longitudinal direction thereof.
Preferably, the second internal conductor is formed with a pair or branch parts led out toward two opposite outside surfaces of the dielectric body, and each of the branch parts is connected to each of a pair of second terminal electrodes.
Preferably, the second internal conductor has a rectangular pattern slightly narrower than the ceramic layer forming the dielectric body, and
the pair of branch parts are formed at one end of the rectangular pattern in the longitudinal direction thereof.
Preferably, the intermediate internal conductor is formed with a pair of branch parts led out toward two opposite outside surfaces of the dielectric body, and each of the branch parts is connected to each of a pair of intermediate terminal electrodes.
Preferably, the intermediate internal conductor has a rectangular pattern slightly narrower than the ceramic layer forming the dielectric body, and
the pair of branch parts are formed at a substantial center of the rectangular pattern in the longitudinal direction thereof.
Preferably, the intermediate internal conductor is further formed with, separate from the pair of branch parts led out toward the two opposite outside surfaces of the dielectric body, a pair of branch parts led out to another two opposite outside surfaces separate from the two outside surfaces, each of these branch parts is connected to each of a pair of the intermediate terminal electrodes, and
the four the outside surfaces of the dielectric body are formed with intermediate terminal electrodes.
Preferably, the intermediate terminal electrodes are formed at the outside surfaces of the dielectric body between the first terminal electrodes and second terminal electrodes.
Preferably, the intermediate terminal electrodes are connected to the ground, while the first terminal electrodes and second terminal electrodes are connected to paths for transmission of signals.
To achieve the above object, according to a second aspect of the present invention, there is provided a multilayer feedthrough capacitor comprising:
a first internal conductor arranged in a dielectric body,
an intermediate internal conductor arranged in the dielectric body and stacked with the first internal conductor via a ceramic layer,
a second internal conductor arranged in the dielectric body and stacked with the intermediate internal conductor via a ceramic layer,
a first terminal electrode formed at an outside surface of the dielectric body and connected to the first internal conductor,
a second terminal electrode formed at the outside surface of the dielectric body and connected to the second internal conductor,
an intermediate terminal electrode formed at the outside surface of the dielectric body and connected to the intermediate internal conductor,
an auxiliary second internal conductor arranged insulated from the first internal conductor on the same plane inside the dielectric body and connected to the second internal conductor via the second terminal electrode, and
an auxiliary first internal conductor arranged insulated from the second internal conductor on the same plane inside the dielectric body and connected to the first internal conductor via the first terminal electrode.
Preferably, the first internal conductor and the second internal conductor have currents passing through them in opposite directions, and the auxiliary first internal conductor and the auxiliary second internal conductor have currents passing through them in opposite directions.
Preferably, inside the dielectric body, the intermediate internal conductor is stacked between the first internal conductor and second internal conductor via the ceramic layers.
Preferably, the first internal conductor and auxiliary first internal conductor are respectively formed with pairs of branch parts led out toward two opposite outside surfaces of the dielectric body, and each of the branch parts is connected to each of a pair of first terminal electrodes.
Preferably, the first internal conductor and auxiliary first internal conductor respectively have rectangular patterns slightly narrower than half of the area of the ceramic layer forming the dielectric body, and
the pairs of branch parts are formed at one ends of the rectangular patterns in the longitudinal direction thereof.
Preferably, the second internal conductor and auxiliary second internal conductor are respectively formed with pairs of branch parts led out toward two opposite outside surfaces of the dielectric body, and each of the branch parts is connected to a pair of second terminal electrodes,
Preferably, the second internal conductor has a rectangular pattern slightly narrower than half of the area of the ceramic layer forming the dielectric body, and
the pair of branch parts are formed at one end of the rectangular pattern in the longitudinal direction thereof.
Preferably, the intermediate internal conductor is formed with a pair of branch parts led out toward two opposite outside surfaces of the dielectric body, and each of the branch parts is connected to a pair of intermediate terminal electrodes.
Preferably, the intermediate internal conductor has a rectangular pattern slightly narrower than the ceramic layer forming the dielectric body, and
the pair of branch parts are formed at a substantial center of the rectangular pattern in the longitudinal direction thereof.
Preferably, the intermediate internal conductor is further formed with, separate from the pair of branch parts led out toward the two opposite outside surfaces of the dielectric body, a pair of branch parts led out to another two opposite outside surfaces separate from the two outside surfaces, each of these branch parts is connected to each of the intermediate terminal electrodes, and
the four the outside surfaces of the dielectric body are formed with intermediate terminal electrodes.
Preferably, the intermediate terminal electrodes are formed at the outside surfaces of the dielectric body between the first terminal electrodes and second terminal electrodes.
Preferably, the intermediate terminal electrodes are connected to the ground, while the first terminal electrodes and second terminal electrodes are connected to paths for transmission of signals.
According to the multilayer feedthrough capacitors according to the first and second aspects of the present invention, in addition to the intermediate internal conductors for grounding, there are first internal conductors and second internal conductors which signals etc. are input and output. Therefore, the capacitors of the present invention have array structures including two feedthrough capacitor elements. Therefore, it is possible to reduce both the noise of the common mode and the differential mode by just one multilayer feedthrough capacitor.
Further, in the first and second aspects of the present invention, currents flow in opposite directions in the first internal conductors and the second internal conductors. Therefore, due to the canceling action of the magnetic fields generated along with the flows of the high frequency currents in opposite directions in these internal conductors, inductance is suppressed, the ESL is further reduced, and the effect of elimination of noise in the high frequency band is improved.
In particular, in the second aspect of the present invention, an auxiliary second internal conductor is also arranged in the plane in which the first internal conductor is arranged and currents flow in opposite directions in these internal conductors. That is, currents flow in opposite directions in the two internal conductors arranged adjoining each other in the same plane. Therefore, the ESL is further reduced, and the effect of elimination of noise in the high frequency band is improved.
Further, in the aspect of the invention where one intermediate terminal electrode is arranged at each outside surface of the dielectric body, for a total of four, the terminal electrodes are arranged optimally at the outside surfaces of the capacitor body. Therefore, it becomes possible to effectively utilize the side surfaces of the capacitor body forming the multilayer feedthrough capacitor. Further, at least four intermediate terminal electrodes are connected to the interconnects of the external ground patterns. Along with this, the inductance at the branch parts of the intermediate internal conductors becomes smaller. As a result, the ESL is further reduced.